In microwave radio communication, higher output power has always been a market requirement for longer distance, higher modulation and higher throughput needs. One way of achieving a higher output power level is to combine two radio-frequency (RF) signals from two channel units into one and keep the two units within the same enclosure to reduce cost, power consumption and size of the field installation. However, there are often small but random frequency and phase offsets between the two channel units, which may cause incoherency between the two respective RF signals. As such, if both channel units were online with the random frequency and phase offsets, each of the two RF signals would be a high level noise to the other one and the receivers on the remote side of the radio link may not be able to recover the transmitted data correctly. Therefore, it is important to improve coherency of the signals in both RF channels in order to achieve high power combining efficiency of such approach.